1. Field of the Invention
This invention relates to a rotary hearth furnace plant for heating granular high-carbon solids, comprising a substantially funnel-shaped hearth, which rotates on a vertical axis and has a central outlet, which is disposed over a rotary table, on which the heated solids are moved by means of blades to an exit.
2. Discussion of Prior Art
Rotary hearth furnace plants of that kind are known from German Offenlegungsschrift No. 21 63 829, German Nos. 22 21 635 and 26 04 667 and the corresponding U.S. Pat. Nos. 3,763,011; 3,740,184 and 3,998,703. They serve, e.g., for coking coal or for heating and calcining petroleum coke. The temperatures of the heated solids lie in the range from 400.degree. to 1400.degree. C., for coal in most cases between 600.degree. and 950.degree. C. and for petroleum coke in most cases between 900.degree. and 1400.degree. C.
In the known rotary hearth furnace plants, a rotary table is used for a continuous discharge of the hot solids flowing to the outlet of the hearth. The center of the rotary tables known from the above-mentioned patent publications is disposed under the conical outlet of the rotary hearth. Stationary, adjustable blades are provided, which move the hot solids of the rotary table outwardly to the rim thereof. The solids are then discharged across said rim through a suitable exit, which is succeeded by cooling and conveying means.
If the rotary table is centrally mounted in known manner, it is not possible to seal the rim of the table against the overlying hood in such a manner that an uncontrolled escape of hot solids across the rim of the table is reliably avoided. This is due to the fact that there must always be a gap between the rim of the rotary table and the stationary hood in order to permit a rotation of the table and a discharge of the hot solids. If hot solids, such as incandescent coke, escape through that gap at a point where a discharge is not desired, the solids may be ignited and this may result in dangerous fires or other risks.
In addition, the hot solids cannot be discharged continuously and uniformly as is desired because the hot solids must be removed by means of a stationary blade from the conical pile which is formed between the conical outlet under the rotary hearth and the rotary table and which rotates at relatively high speed. For this reason the rate at which hot solids are discharged during a rotation of the table at constant speed depends on the angle of repose, which may depend on grading, temperature etc.
For this reason, it is an object of the invention to provide a rotary table which, in the first place, allows the hot solids on the table to leave the table only through the exit which is provided and, in the second place, provides a more uniform discharge rate due to the fact that the discharge rate no longer depends on the angle of repose.